Coal-bed methane is a natural gas extracted from coal seams or adjacent sandstones. In a U.S. Geological Survey Fact Sheet (FS-019-97) published in 1997, it was reported that in the conterminous United States more than 700 trillion cubic feet (TCF) of coal-bed methane exists in place, with perhaps one seventh (i.e., about 100 TCF) economically recoverable with 1997 technology. Commercial production occurs in approximately 10 U.S. basins, including the San Juan, Black Warrior, and Central Appalachian Basins. The exploitation of coal-bed methane is now international with coal-bed gas projects in numerous locations in various countries outside the United States. Methane can be found in coal seams that have not been overly compressed by a large depth of overburden.
Coal seams, particularly at shallow depths, have large internal surface areas that can store large volumes of methane-rich gas; six or seven times as much as a conventional natural gas reservoir of equal rock volume can hold. Since methane-laden coal is found at shallow depths, wells are easy to drill and relatively inexpensive to complete. With greater depth, increased pressure closes fractures (cleats) in the coal, which reduces permeability and the ability of the gas to move through and out of the coal.
Methane bearing coal mined without first extracting the methane gas can give cause to safety and environmental concerns because methane gas is highly flammable and when released into the atmosphere contributes to global warming. According to FS-019-97, methane in the atmosphere has increased at a rate of about 1 percent per year for 15 years prior to the publication of FS-019-97.
Extraction of coal-bed methane, however, carries with it some technological, environmental and worker safety issues and costs. In a conventional natural oil or gas reservoir, for example, methane rich gas lies on top of the oil, which, in turn, lies on top of water. An oil or gas well draws only from the petroleum that is extracted without producing a large volume of water. In contrast, water permeates coal beds, and the resulting water pressure typically traps coal-bed methane within the coal. To produce methane from coal beds, water is typically drawn off to lower the pressure so that methane can flow out of the coal seam and into the well bore and thence to the surface for processing and/or storage, and onward transportation to customers.
A submersible water pump is typically used to pump water from methane bearing coal seams (the terms “seam” and “bed” are regarded here as equivalent terms). The submersible pump is lowered from the surface into a drilled well, and more typically into a drilled well bore at the bottom of the well, to pump out the water. Though submersible pumps are designed to operate with minimum maintenance, there are occasions when the submersible pump must be brought back up to the surface either for maintenance or for replacement with a new submersible water pump.
Extracting a submersible water pump from a CBM well involves considerable hazards. First, water is pumped down into the well to create positive pressure around the well bore at the bottom of the CBM well to stop methane from entering the well and thence making it to the top of the CBM well. The top of the CBM well is then partially removed to allow a work crew to bring the submersible pump to the surface as quickly as possible. In the intervening time between creating positive water pressure around the well bore and getting the submersible water pump to the surface, CBM methane may enter the well bore and make it to the surface, causing a serious hazard for the crew tasked with extracting the submersible water pump.
Thus, there is a strong need for an apparatus and methodology to enable the safe extraction of the submersible water pump without the risk of significant quantities of CBM methane getting to the top of the well.
The Applicant is unaware of inventions or patents, taken either singly or in combination, which are seen to describe the instant invention as claimed.